Muscle revision Flashcards
2 types of muscle fibres
- myocytes
- myofibres
Sarcolemma
- muscle cell membrane
Sarcoplasm
- muscle cell cytoplasm
Sarcomere
- contractile muscle unit formed by myofiibrils
Myofibril
- accumulation of contractile proteins
What does the sarcoplasmic reticulum store?
- calcium
What surrounds myofibres?
- sarcoplasmic reticulum
How does a muscle contract?
- neural signal travels down axon and activates calcium entry terminal axon
- calcium interacts with snare proteins outside acetylcholine vesicles at terminal axon
- this causes release of acetylcholine
- sodium enters the myofibre
- depolarisation current reaches the sarcoplasmic reticulum through connecting tubules
- calcium release within the sarcoplasm
- calcium binds to troponin
- tropomyosin unleashes actin
- contraction begins
Function of sodium in muscle contraction
- speeds up the depolarisation/transmission at the junction
Muscle fuel
- phosphagen system
- glycogen
- fatty acids
- branch aa
- lactate
Phosphagen system
- CK stores & myokinase system
How long does phosphagen system last for?
- 10-20s
Does the phosphagen system use oxygen?
- no
Main energy source for muscle
- glycogen
Use of fatty acids as fuel for muscles
- endurance (sustained exercise)
Branch aa fuel source
- gluconeogenesis & tricarboxylic acid cycle
Is branch aa effective?
- has to go through gluconeogenesis so consumes more energy to produce glucose
- not effective
How does lactate provide a source of fuel?
- NAD production
- liver cori cycle
Does production of lactate increase or decrease the pH of cells?
- decrease
What fibre type is aerobic?
- type I
What fibre types are aerobic?
- type IIa
- type IIx
What fibre type has the fastest contraction time?
- type IIx
What fibre type has the most resistance to fatigue?
- type I
What type of exercise are type IIa fibres used for?
- long term anaerobic activity
What type of exercise are type IIx fibres used for?
- short term anaerobic activty
Which type of fibre has the shortest duration of action?
- type IIx
– less than 5 mins
Which type of fibre has the longest duration of action?
- type I
- hourse
Which type of fibre has the most power produced?
- type IIx
Which type of fibre has the lowest power produced?
- type I
Which type of fibre demands the most mitochondrial activity?
- type I
Major source of fuel of type I fibres
- creatinine phosphate
- glycogen
Major source of fuel for type IIx fibres
- ATP
- creatinine phosphate
- glycogen
Examples of type I muscle fibres
- myocardium
- core muscles (posture)
- extensors e.g. triceps, neck
- abaxial muscles
- intercostal muscles
Fibre type that should be prioritised if you want to train for speed
- type II
Fibre type that should be prioritised if you want to train for endurance
- type I
What oxidation is important for sustained exercise?
- fatty acid
Fastest source of energy
- ATP-PCr system
What happens if muscles work too hard?
- ROS mitochondrial respiratory chain
- Acetyl-carnitines in fatty acid oxidation
- lactate in glycolysis
3 hardest working structures in the body
- heart (muscles)
- brain
- liver
What does increased ROS do?
- breaks down cell membrane
- impairs the function of the mitochondria
Acetyl-carnitines
- intermediate product of fatty acid oxidation
Mechanisms for counteracting oxidative stress
- vitamin E
- cysteine
- Q10
Role of vitamin E
- sarcolemma repair
Best marker for muscle disease
- CK
2 markers of muscle disease
- CK
- AST
How to differentiate between CK & AST in horses
- SDH
- GGT
SDH
= sorbitol dehydrogenase
What equid species is GGT commonly high in?
- donkeys
When does CK peak?
- 6h
When does AST peak?
- 24h
How long does it take for AST to come down?
- weeks
Why is CK not elevated in cardiac disease?
- lab tests only measure MSK CK
- so not detecting the isomer of cardiac CK
What marker of cardiac muscle damage do lab tests look for?
- cardiac troponin
Why is MSK troponin not tested for?
- no need
- CK a better marker
Is there an injury if persistent AST & CK are seen?
- yes
If there’s persistent AST does that mean there’s persistent injury?
- no
2 types of muscle injury
- extertional
- non-extertional
Can cardiac troponin be naturally increased after exercise?
- yes
Classic clinical presentation of a myopathy
- stiff pelvic limbs
- low head carriage
- sweaty
